For a quantum dot film used by a backlight module, red and green quantum dots on the quantum dot film may be excited by a blue LED lamp so as to emit light. For a display substrate of a small size, its light guide plate is provided with screen dots having specific structures, which change a light propagation direction to prevent a total reflection within the light guide plate so as to enable the light guide plate to have a good light guide effect. For a display substrate of a medium size or a large size, its light guide plate is provided with ink screen dots, and a scattering function of the ink is used to prevent the total reflection within the light guide plate so as to enable the light guide plate to have a good light guide effect. However, for both the above two manners, it is required to manufacture the screen dots in the light guide plate. Therefore, the process is complex and the cost is high.